Feed conversion rate and estimated energy balance of free grazing Iberian pigs

Abstract: A direct in situ observation method has been used, observing ingestive bites taken by continuously monitored Iberian pigs (10 uninterrupted hours, from 08:30 to 18:30) to calculate intake of acorns and grass and grazing activity during the fattening period in the dehesa (cleared Mediterranean forest like savannah) from November first to the end of December. The obtained results, together with measurements of weight gain, have been used to propose a new method for calculating stocking rate capacity. 60 grazing days have been studied corresponding to different randomly chosen Iberian pigs (110.2±1.3kg of average initial LW) during 2months. The results show a daily intake of 56.4±2.34MJ ME from grass and acorns, of which acorns accounted for 90.42% (2.92±0.13kg of kernel DM and 0.49±0.04kg of grass DM); to do so pigs walk 3.9±0.18km in 369.0±7.8min of activity which happens at an average temperature of 7.6±0.2°C. The daily expenditure of ingested energy is divided as follows: 13.8±0.18MJ for the resting metabolism (54.1%±0.44); 5.5±0.14MJ for thermoregulation (21.5%±0.29); 6.3±0.15MJ for grazing, divided in displacement (8.0%±0.32) and standing (16.4%±0.25) during the activity. The total energy cost is therefore 25.7±0.38MJ ME, which equals 51.2%±2.71 of the ingested ME. ME available for production was 30.7±2.33MJ per pig and day, equivalent to 0.8±0.06MJ/kg LW0.75 per day. The total heat losses were 31.8±0.59MJ per pig and day. The corresponding ratios are: 253.0±13.05g/kg DM for gain/feed, 15.3±0.79g/MJ for gain/ME intake and 1.4±0.06MJ/kg LW0.75. There are not significant differences between both sexes. With an average daily weight gain of 0.79±0.03kg, the conversion rate of the ME consumed as grass and acorns is 56.4±2.34MJ ME (corresponding to 4.0±0.29 Kg kernel DM and 0.7±0.08kg of grass DM). To ingest that amount of energy pigs have to use 10.5±0.75kg of entire acorns to shell these. Bearing in mind that the annual production of acorns of an average adult evergreen oak (Q. ilex rotundifolia) acorn production is very close to this amount, it could be established that pig feed conversion rate (FCR) for acorn equals the total acorn production from one adult tree. So stocking rate may be estimated by dividing the number of adult oaks of a dehesa by the expected weight gain; and it could be established that stocking rate should be <1pig/ha of dehesa to gain the minimum standard of 46kg only grazing natural resources. [Copyright &y& Elsevier]